|I reached out to Sylvia Smith with my concerns about repotting. Basically, would I do more damage to my trees by repotting after this horrible cold weather? This is what she said. (I hope she doesn't mind me sharing.)
We keep our trees in the cold frame so we do not bury them as deeply as others if they are left outside. The few that we did leave out are either in boxes or deep plastic nursery pots and they were all nestled under the benches and not really mulched except for a few fall leaves that I scooped together for a few. That said, if you have any doubts on the health of the trees, simply do a top soil change. If drainage is poor, go a bit deeper. You can almost without fail go down to half the root ball to do this on a potted tree whether in a bonsai pot or growing container.
Our plan on what was left out is the same as our advice to members in the Dallas newsletter, wait until they push to repot. Then you should be able to see the difference between live and dead roots. If the tree looks weak or had branch damage, only do a top soil change.The hardiness is most important when storing trees but sometimes things don't go as planned and after a freeze it's pretty much a mute point. You either did it or you didn't. Even trees that are usually hardy in the cold can start off weak from insects, fungal or root issues and a cold spell can take them over the edge. If trees are left outside it is imperative that they are watered thoroughly prior to a freeze so they can freeze as a solid mass that melts as opposed to freezing dry. This will most definitely be a cause for dead roots.
Hope this all helps. Only you know what went on in your own micro-climate and the advice given from all of us hopefully will help you piece your puzzle together. I will begin repotting this Friday and will post some advice on our FB and Instagram pages (Dallas Bonsai Society).
Be well and stay safe.